Composition for direct-current cathodic electrolysis, lubrication-film-equipped metal material, and production method therefor

ABSTRACT

A composition for direct-current cathodic electrolysis. The composition is capable of forming a lubrication-film-equipped metal material exhibiting excellent lubrication properties and excellent chemical conversion properties after degreasing. This composition for direct-current cathodic electrolysis includes: (A) at least one metal ion selected from the group consisting of typical metal ions (excluding zinc ion) having a valency of at least 2 and rare-earth-element ions, or a complex thereof; (B) an organic acid compound including, in the molecule thereof, a carboxyl group, and a straight-chain alkylene group having at least 4 carbon atoms; and (C) water.

TECHNICAL FIELD

The present invention relates to compositions for direct-current cathodic electrolysis, particularly to a composition for direct-current cathodic electrolysis containing a specified metal ion and an organic acid compound.

The present invention also relates to a metal material having a lubricating film as obtained using a composition for direct-current cathodic electrolysis, and a production method thereof.

BACKGROUND ART

Metal materials are used for a variety of constructs. For example, ferrous materials originally having plate-, wire- and bar-shapes are subjected to forging processes such as pressing, drawing, cutting and stamping to form parts of constructs, and formed parts are joined by welding or an adhesive, whereby constructs are assembled to have general shapes. Through a rustproofing process and various painting processes (painting methods), such intermediate constructs are formed into products with taking design properties into account. In some cases, electronic components or interior components are installed in the products thus formed, and final products are shipped.

Such forging processes of materials require lubrication, and various related techniques have been proposed. For instance, Patent Literature 1 discloses, as a method for forming a lubricating film, a technique involving forming a chemical conversion film by carrying out cathodic electrolysis using an electrolytic solution containing zinc ions, phosphate ions and nitrate ions, and thereafter bringing the film into contact with a water- or oil-based lubricant.

CITATION LIST Patent Literature

Patent Literature 1: JP 2000-144494 A

SUMMARY OF INVENTION Technical Problems

Meanwhile, in recent years, there is a need for various types of chemical conversion treatments that can be easily carried out after working with metal materials. More specifically, it is desired to, after working with a metal material having a lubricating film, remove the lubricating film to allow various types of chemical conversion treatments (e.g., zinc phosphate treatment and metal oxide treatment) to be easily carried out. In other words, lubricating films are required to, while having excellent lubrication, be removable in a manner allowing excellent chemical conversion properties to be achieved after degreasing. In particular, film removal treatment, which is performed to prepare for a painting process, is required to be easily accomplished by degreasing treatment that is commonly carried out before chemical conversion treatment.

The present inventors have formed lubricating films with a method described in Patent Literature 1 and studied the characteristics (lubrication and chemical conversion properties after film removal) of the resulting lubricating films. The study has revealed that chemical conversion films formed after degreasing treatment exhibit unevenness, and thus the lubricating films fail to sufficiently achieve both lubrication and chemical conversion properties after degreasing. In particular, with an embodiment of Patent Literature 1, a zinc phosphate film and/or a reaction type soap film formed on a metal material cannot be removed by common degreasing treatment and remains, and therefore, chemical conversion treatment that is subsequently carried out does not proceed well.

In view of the situation as described above, an object of the present invention is to provide a composition for direct-current cathodic electrolysis capable of forming a metal material having a lubricating film that has excellent lubrication and also allows excellent chemical conversion properties to be achieved after degreasing.

Another object of the present invention is to provide a method of producing a metal material having a lubricating film using a composition for direct-current cathodic electrolysis, as well as a metal material having a lubricating film.

Solution to Problems

The present inventors have made an intensive study on the foregoing objects and as a result found that a lubricating film exhibiting desired characteristics can be yielded by performing cathodic electrolysis using a composition for direct-current cathodic electrolysis containing a specified metal ion or its complex, and a specified organic acid compound.

Specifically, the foregoing objects can be achieved by the characteristic features below.

(1) A composition for direct-current cathodic electrolysis, comprising:

(A) at least one type of metal ion, or its complex, selected from the group consisting of divalent or higher valent main group metal ions (excluding zinc ion) and rare earth element ions;

(B) an organic acid compound having a carboxyl group and a linear alkylene group with 4 or more carbon atoms per molecule; and

(C) water.

(2) The composition for direct-current cathodic electrolysis according to (1), wherein the metal ion or its complex (A) includes at least one type of metal ion, or its complex, selected from the group consisting of magnesium ion, calcium ion, aluminum ion, yttrium ion and lanthanoid metal ions. (3) The composition for direct-current cathodic electrolysis according to (1) or (2), wherein the organic acid compound (B) includes an aliphatic monocarboxylic acid having a linear alkylene group with 4 or more carbon atoms or an aliphatic dicarboxylic acid having a linear alkylene group with 4 or more carbon atoms. (4) The composition for direct-current cathodic electrolysis according to any one of (1) to (3), having a pH of 3.5 to 12.5. (5) A method of producing a metal material having a lubricating film, comprising a step of forming a lubricating film on a surface of a metal material by immersing the metal material in the composition for direct-current cathodic electrolysis according to any one of (1) to (4) and performing cathodic electrolysis using direct current with the metal material serving as a cathode. (6) A metal material having a lubricating film produced by the method of producing a metal material having a lubricating film according to (5). (7) A metal material having a lubricating film comprising a metal material and a lubricating film disposed on a surface of the metal material,

wherein the lubricating film includes:

at least one type of metal element selected from the group consisting of divalent or higher valent main group metal elements (excluding elemental zinc) and rare earth elements; and

an organic acid compound having a carboxyl group and a linear alkylene group with 4 or more carbon atoms per molecule, and/or its salt, and

wherein in a depth profiling analysis of the lubricating film by glow discharge optical emission spectrometry as conducted on the lubricating film from its surface opposite from a side facing the metal material in a direction toward the metal material, a ratio (Im/Is) between a peak intensity derived from elemental carbon at the surface of the lubricating film opposite from the side facing the metal material (Is) and a peak intensity derived from elemental carbon at a middle level in the lubricating film corresponding to a half of a whole thickness of the lubricating film from the surface opposite from the side facing the metal material (Im) is less than 1.0.

(8) The metal material having a lubricating film according to (6) or (7), further comprising, on the lubricating film, an oil layer containing an oil component.

Advantageous Effects of Invention

The present invention can provide a composition for direct-current cathodic electrolysis capable of forming a metal material having a lubricating film that has excellent lubrication and also allows excellent chemical conversion properties to be achieved after degreasing.

In addition, the present invention can provide a method of producing a metal material having a lubricating film using a composition for direct-current cathodic electrolysis, and a metal material having a lubricating film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing one embodiment of a metal material having a lubricating film according to the invention.

FIG. 2 is a schematic cross-sectional view showing another embodiment of a metal material having a lubricating film according to the invention.

FIGS. 3(A) and 3(B) are schematic views of a high-speed deep drawing tester used in a lubrication evaluation (No. 2) for Examples.

DESCRIPTION OF EMBODIMENTS

A composition for direct-current cathodic electrolysis (treatment solution for direct-current cathodic electrolysis) and a metal material having a lubricating film as well as a production method thereof according to the invention are described below in detail. It should be noted that the figures for this invention illustrate schematic views and the relative thicknesses of layers and the like do not necessarily reflect actual ones.

One characteristic of the invention is to perform cathodic electrolysis using a composition for direct-current cathodic electrolysis containing a specified metal ion or its complex and a specified organic acid compound, as described above.

A typical method of surface treatment is plating that is carried out by cathodic electrolysis for depositing a metal on a material to be treated. In the present invention, while a material to be treated is used as the cathode, the metal ions or their complexes which are hardly deposited as a metal are used as a component of the composition. That is, the metal ions or their complexes used in the invention are hardly reduced as a metal in an aqueous system, and easily become hydroxides, hydrous oxides and/or oxides containing the metal ions.

The present invention employs a method of forming a film by direct-current cathodic electrolysis. First, when cathodic electrolysis is performed, due to electrophoresis, the metal ions or their complexes are concentrated in the vicinity of a metal material, which is a material to be treated. At that time, as a part of reduction reaction involving consumption of electrons released from the material to be treated, hydrogen ions are consumed, while hydroxide ions increase. For instance, when electrolysis of water proceeds, a hydrogen gas is generated from a surface of a metal material, which is a material to be treated, and therefore, the increase in pH is prompted on the surface of the metal material. As a result, the metal ions or their complexes concentrated form insoluble salts (oxides, hydroxides or hydrates) and are deposited on the surface of the metal material. In a region where the metal ions or their complexes have been deposited, a resulting film can be easily removed by commonly-used film removal treatment such as degreasing treatment, which facilitates chemical conversion treatment to be subsequently carried out.

Meanwhile, the organic acid compound contains a carboxyl group and therefore exhibits electrophoresis, namely, moves away from the metal material. Consequently, the organic acid compounds are hardly deposited on the surface of the metal material. In particular, since the organic acid compounds exhibit a higher ionicity with a higher pH in the vicinity of the metal material, the phenomenon above is seen more remarkably. Thus, the organic acid compounds are hardly deposited on the surface of the metal material in the initial stage of cathodic electrolysis; and as the electrolysis proceeds, the organic acid compounds gradually form salts in combination with the metal ions or their complexes, oxides and hydroxides that contain the metal ions, and other components. This is probably the way how composite salts of the organic acid compounds and the metal ions are deposited on the surface of the metal material. In other words, the organic acid compounds are concentrated on an exposed surface side (i.e., an opposite surface from the side facing the metal material) of a lubricating film. Thus, the organic acid compounds excellent in lubrication are present in a large amount at a surface of a lubricating film, resulting in excellent lubrication.

As described above, when direct-current cathodic electrolysis is performed using an aqueous composition containing a metal ion or its complex and an organic acid compound, the hydroxide ion concentration increases on a surface of a metal material, and the precipitation equilibrium between the metal ion and the organic acid compound is disturbed, leading to deposition of a lubricating film. A process of forming a lubricating film as above is greatly different from conventional processes of forming lubricating films.

The use of the composition as above is preferred in terms of industrial productivity because high-temperature treatment can be omitted and treatment is completed with one step in the manufacture of lubricating films. Furthermore, the use of the composition as above is preferred in cost and productivity because a resulting lubricating film exhibits desired effects even with a small thickness.

In the following description, components (metal ion or its complex (A), organic acid compound (B) and water (C)) constituting a composition for direct-current cathodic electrolysis (hereinafter also simply called “composition”) are described in detail, and then a method of producing a metal material having a lubricating film using the composition is described in detail.

<Metal Ion or Its Complex (A)>

The composition contains at least one type of metal ion, or its complex, selected from the group consisting of divalent or higher valent main group metal ions (excluding zinc ion) and rare earth element ions (A) (hereinafter also called “metal ion (A)” that represents a concept covering a metal ion and its complex). The metal ion (A) is to be a metal oxide or a metal hydroxide, or a complex with the organic acid compound (B), which will be described later, to constitute a lubricating film in cathodic electrolysis.

Examples of main group metal ions (ions of main group metal elements) include; ions of elements in Group 2 of the periodic table, such as beryllium, magnesium, calcium, strontium, barium and radium (alkaline earth metal ions); ions of elements in Group 12 of the periodic table, such as cadmium and mercury (excluding zinc ion); ions of elements in Group 13 of the periodic table, such as aluminum, gallium, indium and thallium; ions of elements in Group 14 of the periodic table, such as germanium, tin and lead; ions of elements in Group 15 of the periodic table, such as antimony and bismuth; and ions of elements in Group 16 of the periodic table, such as polonium.

The rare earth element ions refer to ions of rare earth elements, and represent a concept covering yttrium ion (ion of yttrium element), scandium ion (ion of scandium element) and lanthanoid metal ions.

The lanthanoid metal ions (ions of lanthanoid metal elements) refer to ions of metal elements of the lanthanoid series, and more specifically, ions of elements such as lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

Of these, magnesium ion, calcium ion, aluminum ion, yttrium ion and lanthanoid metal ions are preferred, and magnesium ion, calcium ion and aluminum ion are more preferred because such ions allow the lubrication of a lubricating film and/or chemical conversion properties after degreasing to be more excellent (hereinafter also simply referred to “because the effect(s) of the invention can be more excellent”).

For the metal ion (A), those metal ions may be used singly or in combination of two or more.

A complex of metal ion as above refers to a complex containing any of the foregoing metal ions (organic complex). It is preferable for the complex to contain a chelating agent (complexing agent). The chelating agent does not contain the organic acid compound (B) to be described later.

The type of chelating agent is not limited as long as it serves to chelate the metal ion and does not impair the effects of the invention. Applicable chelate agents include: organic acids such as gluconic acid, citric acid and succinic acid, as well as salts thereof; organophosphorus compounds; and aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA), as well as salts thereof. Of these, aminopolycarboxylic acids and salts thereof are preferred because the effect(s) of the invention can be more excellent. While condensed phosphates such as sodium tripolyphosphate may be used as a chelating agent, such condensed phosphates are preferably not contained in the composition because they readily form salts with metal ions and are hard to control.

The aminopolycarboxylic acids refer to chelating agents each having an amino group and plural carboxyl groups per molecule. Specific examples thereof include EDTA (ethylenediaminetetraacetic acid), HEDTA (hydroxyethyl ethylenediaminetriacetic acid), NTA (nitrilotriacetic acid), DTPA (diethylenetriaminepentaacetic acid) and TTHA (triethylenetetraminehexaacetic acid). Exemplary salts of aminopolycarboxylic acids include, but not limited to, ammonium salts, sodium salts and potassium salts of the above-mentioned compounds.

A method of providing the metal ion or its complex to the composition is not limited, and one example thereof is a method in which an inorganic component such as a salt containing the metal ion (e.g., carbonate, hydrogencarbonate, acetate, formate, nitrate, sulfate, borate), an oxide, a hydroxide or a halide (e.g., fluoride), or a complex (organic complex) containing the metal ion, is added to water. When a metal material having a lubricating film is stored for a long time or in a hot and humid environment, it is preferable for the composition not to contain a chloride in order to avoid rusting.

The concentration of the metal ion or its complex in the composition is not limited, and is preferably 50 to 50000 ppm by mass, and more preferably 500 to 10000 ppm by mass because the effect(s) of the invention can be more excellent.

When two or more types of metal ions (A) are used, it is preferable that the total concentration of metal ions (A) fall within the foregoing ranges.

When a complex of the metal ion is used, it is preferable that the amount of metal ion present in the complex fall within the foregoing ranges.

<Organic Acid Compound (B)>

The organic acid compound (B) is a compound having a carboxyl group and a linear alkylene group with 4 or more carbon atoms per molecule. The organic acid compound (B) interacts with the metal ion (A) via a carboxyl group to form a complex, which is to be incorporated into a lubricating film. A hydrocarbon skeleton in the organic acid compound (B) contributes to the lubrication.

The organic acid compound (B) contains a carboxyl group or groups, the number of which is not limited. Monocarboxylic acids each having a single carboxyl group and dicarboxylic acids each having two carboxyl groups are preferably used because the effect(s) of the invention can be more excellent.

The organic acid compound (B) contains a linear alkylene group with 4 or more carbon atoms. The linear alkylene group is a group expressed by Formula (1) below. n represents an integer of 4 or more.

*—(CH₂)_(n)—*  Formula (1)

n represents an integer of 4 or more. In particular, n is preferably an integer of 4 to 17 and more preferably 4 to 8 because the effect(s) of the invention can be more excellent. A longer straight chain in an alkylene group means a higher fatty acid and results in more excellent lubrication.

In the above formula, * is a bonding position.

Preferred examples of the organic acid compound (B) include aliphatic monocarboxylic acids having a linear alkylene group with 4 or more carbon atoms and aliphatic dicarboxylic acids having a linear alkylene group with 4 or more carbon atoms. Preferred examples of such aliphatic monocarboxylic acids and aliphatic dicarboxylic acids include aliphatic monocarboxylic acids expressed by Formula (1) and aliphatic dicarboxylic acids expressed by Formula (2).

[Chemical Formula 1]

R—COOH  Formula (1)

HOOC-L-COOH  Formula (2)

In Formula (1), R is an alkyl group having, as a substructure, a linear alkylene group with 4 or more carbon atoms. The number of carbon atoms in an alkyl group is not limited as long as it is 4 or more, and is preferably 4 to 18, more preferably 4 to 16 and even more preferably 5 to 12 because the effect(s) of the invention can be more excellent.

The alkyl group is not limited as long as it has, as a substructure, a linear alkylene group with 4 or more carbon atoms. For instance, preferable examples of aliphatic monocarboxylic acids expressed by Formula (1) include compounds expressed by Formula (1-1) below.

R₁-L-COOH  Formula (1-1)

R₁ represents an alkyl group. L represents a linear alkylene group with 4 or more carbon atoms. The alkyl group expressed by R₁ may be a linear or branched group. While the number of carbon atoms in R₁ is not limited, the sum of carbon atoms in R₁ and L preferably falls within the foregoing range (4 to 18).

The number of carbon atoms in an alkylene group expressed by L is preferably 4 or more, more preferably 4 to 17 and even more preferably 4 to 8.

In Formula (2), L represents a linear alkylene group with 4 or more carbon atoms. The number of carbon atoms in an alkylene group is not limited as long as it is 4 or more, and is preferably 5 or more, and more preferably 7 or more because the effect(s) of the invention can be more excellent. The upper limit of the number is preferably 16 or less in terms of handleablity, but not limited thereto.

Exemplary aliphatic monocarboxylic acids include hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid and octadecanoic acid.

Exemplary aliphatic dicarboxylic acids include hexanedioic acid (adipic acid), heptanedioic acid (pimelic acid), octanedioic acid (suberic acid), nonanedioic acid (azelaic acid), decanedioic acid (sebacic acid), undecanedioic acid, dodecanedioic acid, tridecanedioic acid (brassylic acid), hexadecanedioic acid and octadecanedioic acid.

The concentration of the organic acid compound (B) in the composition is not limited, and is preferably 50 to 50000 ppm by mass, and more preferably 500 to 10000 ppm by mass because the effect(s) of the invention can be more excellent.

When two or more types of organic acid compounds (B) are used, it is preferable that the total concentration of organic acid compounds (B) fall within the foregoing ranges.

<Water (C)>

The composition contains water as a solvent.

The content of the water (C) in the composition is not limited, and is preferably not less than 65% by mass and more preferably not less than 75% by mass with respect to the total weight of the composition because the handleability is good and the effect(s) of the invention can be more excellent. The upper limit of the content is in most cases, but not limited to, not more than 99% by mass.

<Other Components>

The composition may contain other components than the foregoing components (metal ion or its complex (A), organic acid compound (B) and water (C)).

For instance, a chelating agent mentioned above may be optionally added to the composition.

The pH of the composition containing the foregoing components is not limited, and is preferably 3.5 to 12.5 and more preferably 4.0 to 10.0 because the effect(s) of the invention can be more excellent. The direct-current cathodic electrolysis of the invention is less likely to cause etching; however, for instance, when a metal material is rinsed with water after cathodic electrolysis, a part of the composition is slightly taken away, and the composition at a lower pH may be more likely to cause the corrosion of facilities as well as the corrosion of materials in a rinsing process. In addition, if the composition remains on a metal material as a contaminated composition, this may adversely affect resulting steel during storage. In view of the above factors, it is particularly preferable for the composition to have a pH of 6.0 to 9.0.

The pH of the composition can be adjusted with any of known acids (e.g., hydrochloric acid, nitric acid, formic acid, acetic acid, sulfonic acid and hydrofluoric acid) and/or alkalis (e.g., sodium compounds, potassium compounds, ammonia, and amine compounds).

The method of producing the composition is not limited, and any known method is applicable. One exemplary method is a method in which a compound containing the metal ion (A) and the organic acid compound (B) are added to water (C), and the mixture is stirred.

The composition is used in direct-current cathodic electrolysis, as described later. In other words, the composition is used for subjecting a metal material, which is a material to be treated, to cathodic electrolysis using direct current.

<Method of Producing Metal Material Having Lubricating Film>

A method of producing a metal material having a lubricating film by using the composition is described below in detail.

The method of producing a metal material having a lubricating film involves a step of forming a lubricating film on a surface of a metal material by immersing the metal material in the composition for direct-current cathodic electrolysis and performing cathodic electrolysis using direct current with the metal material serving as the cathode. As a consequence of this step, a lubricating film having the component composition to be described later can be yielded on a metal material.

The type of metal material used in this step is not limited, and examples of applicable metal materials include cold rolled steel sheets (SPC materials), hot rolled steel sheets (SPH materials), rolled steels for general structure (SS materials), carbon steels (SC materials), various alloy steels, stainless steels, Al or alloys thereof, Mg or alloys thereof, Cu or alloys thereof, Zn or alloys thereof, nickel-based alloys, and cobalt-based alloys. Metal materials may take on, in addition to a sheet shape, any of coil, bar, band and tube shapes, shapes of cast and forged products, and bearing shapes, and any other shapes may be applied.

A surface of a metal material may optionally be degreased and cleaned in advance.

Cathodic electrolysis may be performed by any known method as long as the method uses a metal material, which is a material to be treated, as the cathode. Typically, a metal material is immersed in the composition, and voltage is applied across the cathode and an insoluble anode. Exemplary insoluble electrodes that may be used include a platinum electrode, a stainless steel electrode and a lead electrode.

The current density is not limited, and is preferably 0.01 to 100 A/dm² and more preferably 0.05 to 50 A/dm² because the effect(s) of the invention can be more excellent.

The amount of supplied current is not limited, and is preferably 5 to 300 C/dm² and more preferably 15 to 180 C/dm² because the effect(s) of the invention can be more excellent.

The temperature of the composition is not limited, and is preferably 15° C. to 40° C. and more preferably 20° C. to 35° C. because a lubricating film is deposited more efficiently. As described above, contrary to the related art, the composition need not be kept at high temperature in the present invention. The temperature of the composition may vary due to circulating heat of a pump or ambient air in the summer.

After cathodic electrolysis, a metal material is taken out from the composition, and a step of washing the metal material with water may be optionally carried out.

After the washing step, a drying step of performing drying treatment may optionally be carried out.

<Metal Material Having Lubricating Film>

As shown in FIG. 1, a metal material 10 having a lubricating film as obtained by the foregoing method includes a metal material 12 and a lubricating film 14 disposed on a surface of the metal material.

The type of the metal material 12 is as described above.

A lubricating film is a film deposited through cathodic electrolysis in the composition. A lubricating film contains: at least one type of metal element selected from the group consisting of divalent or higher valent main group metal elements (excluding elemental zinc) and rare earth elements; and an organic acid compound having a carboxyl group and a linear alkylene group with 4 or more carbon atoms per molecule, and/or its salt.

The metal element or elements present in a lubricating film are derived from metal ions in the composition. The types of metal elements are as mentioned above in relation to the metal ion.

The metal elements are not limited for their state in a lubricating film, and may be present in the form of, for example, oxides or hydroxides of metals.

The metal element content in a lubricating film is not limited, and is preferably not less than 0.05 g/m², more preferably 0.1 to 5 g/m², and even more preferably 0.1 to 3 g/m² because the effect(s) of the invention can be more excellent.

An organic acid compound present in a lubricating film is the above-mentioned organic acid compound in the composition. The organic acid compound in the composition and the metal element(s) are deposited as a lubricating film in cathodic electrolysis. Examples of salts of organic acid compounds include salts resulting from the above-mentioned organic acid compounds and the above-mentioned metal ions.

The content of the organic acid compound or its salt in a lubricating film is not limited, and is preferably 0.05 to 3 g/m² and more preferably 0.1 to 1 g/m² because the effect(s) of the invention can be more excellent.

In the case of a salt of an organic acid compound, only the organic acid compound portion is considered in calculating the content.

In a depth profiling analysis of a lubricating film by glow discharge optical emission spectrometry as conducted on a lubricating film from its surface opposite from the side facing a metal material in a direction toward the metal material, the ratio (Im/Is) between the peak intensity derived from elemental carbon at the surface of the lubricating film opposite from the metal material side (Is) and the peak intensity derived from elemental carbon at the middle level in the lubricating film corresponding to a half of the whole thickness of the lubricating film from the surface opposite from the metal material side (Im) is less than 1.0. In particular, the ratio (Im/Is) is preferably not more than 0.5 and more preferably not more than 0.2. The lower limit of the ratio is in most cases not less than 0.05 for production procedure reasons, but not limited thereto.

To be more specific, referring to FIG. 1, the ratio (Im/Is) between the peak intensity derived from elemental carbon at a surface level 14A of the lubricating film 14 (Is) and the peak intensity derived from elemental carbon at a middle level 14B of the lubricating film 14 (Im) is less than 1.0. That is, the peak intensity (Is) is higher than the peak intensity (Im). The peak intensity derived from elemental carbon at the surface level 14A (Is) refers to the magnitude of the peak derived from elemental carbon at the surface of the lubricating film 14 as obtained by glow discharge optical emission spectrometry. The peak intensity derived from elemental carbon at the middle level 14B (Is) refers to the magnitude of the peak derived from elemental carbon at the level in the lubricating film 14 corresponding in depth to a half of the whole thickness of the lubricating film 14 from the surface (surface level 14A) opposite from the metal material 12 side toward the metal material 12 (i.e., at a cross-sectional region at the middle level in the thickness direction of the lubricating film 14), as obtained by glow discharge optical emission spectrometry.

At a ratio (Im/Is) of 1.0 or more, the effect(s) of the invention is poor.

The peak intensity derived from elemental carbon as above can be measured by a Marcus-type glow discharge optical emission spectrometer (commonly called “GDS”; JY-5000RF, available from HORIBA).

The concentration distribution of elemental carbon as above is generated in a lubricating film probably because, in cathodic electrolysis, a film of an oxide or a hydroxide of a metal derived from metal ions is first deposited on a metal material, whereafter organic acid compounds are gradually deposited, as described above.

In one preferred example of a lubricating film, the elemental carbon content (determined based on the peak density) gradually decreases from the surface of a lubricating film toward the level corresponding in depth to a half of the whole thickness of the lubricating film.

The thickness of a lubricating film is not limited, and is preferably 0.5 to 10 μm and more preferably 0.5 to 5 μm because the effect(s) of the invention can be more excellent.

One preferred example of a metal material having a lubricating film is a metal material 100 having a lubricating film, in which an oil layer 16 containing an oil component is formed on a lubricating film 14 as shown in FIG. 2. The provision of the oil layer 16 improves the lubrication.

Such an oil layer is preferably a lubricating oil layer composed of lubricating oil containing a lubricating component, and also may be an anti-rust oil layer composed of anti-rust oil containing a lubricating component. For an oil layer, lubricating or anti-rust oil may be used as it is.

The coating weight of oil layer is not limited, and is preferably 0.1 to 3.0 g/m², more preferably 0.3 to 2.0 g/m², and even more preferably 0.5 to 1.5 g/m² because this results in more excellent lubrication and removability.

The coating weight can be measured by, for example, a surface carbon analyzer.

Such metal materials each having a lubricating film as described above exhibit excellent lubrication, and also allow a lubricating film to be readily removed by degreasing treatment that is applied in preparation for a painting process and commonly carried out before chemical conversion treatment. Consequently, various chemical conversion treatments can be successfully performed on surfaces of metal materials having undergone the degreasing treatment as film removal treatment.

In other words, such metal materials each having a lubricating film can go through tough forming processes such as deep drawing, ironing and stretch drawing, and are then subjected to degreasing treatment which allows various chemical conversion treatments such as painting to successfully proceed.

EXAMPLES

The present invention is described in detail below with reference to Examples, which by no means limit the scope of the present invention.

(Cleaning Method of Wire Rods and Cold Rolled Steel Sheets (Hereinafter Also Called “SPC Materials”))

In Examples and Comparative examples described below, metal wire rods and cold rolled steel sheets were used as test pieces. Wire rods for use were prepared by cutting SWRM 45 having a diameter of 3.5 mm and a length of 300 mm to a diameter of 3 mm over a portion extending 100 mm from one end, followed by surface cleaning to be described later. Cold rolled steel sheets for use were 120 mm wide, 160 mm long and 0.8 mm thick, which were subjected to surface cleaning to be described later.

For use in Examples and Comparative Examples, the wire rods and the cold rolled steel sheets were subjected to surface cleaning with a degreasing agent in order to remove oil and dirt on the surfaces.

To be more specific, a degreasing agent (FINECLEANER E2001, available from Nihon Parkerizing Co., Ltd.) was heated to 43° C., and the wire rods and the cold rolled steel sheets were immersed in the degreasing agent for 3 minutes to thereby remove oil and dirt on the surfaces. Subsequently, the degreasing agent was washed away from the wire rods and the cold rolled steel sheets with clean water of Hiratsuka-city, and then water was removed from the wire rods and the cold rolled steel sheets by an air blower.

(Method of Measuring Deposition Amounts)

The deposition amounts of metal elements and organic acid compounds in lubricating films produced in Examples and Comparative Examples to be described below were evaluated in accordance with the following procedures.

In cases where a test piece was a wire rod, since a film was formed on each wire rod in a trace amount, the same compositions and the same methods of direct-current cathodic electrolysis as those for surface treatments of the wire rods were used to deposit, on SPC material, the same lubricating films as those deposited on the wire rods, and the deposition amounts of components in the lubricating films thus deposited on the SPC materials were measured. For the anode, an insoluble anode (DSE for oxygen evolution, available from De Nora Permelec Ltd.) was used.

For metal elements, the intensities of metal elements were measured by X-ray fluorescence (with ZSX Primuth II, available from Rigaku Corporation), and the calibration curve obtained from the intensity and the amount was used to calculate the deposition amount (g/m²).

For organic acid compounds, the test pieces were heated at 500° C. for 180 seconds by means of a carbon analyzer (RC-412, available from LECO Corporation) to burn and turn organic acid compounds into carbon dioxides, and the deposition amounts of carbon were obtained. Then, the deposition amount (g/m²) of each organic acid compound was calculated from the thus-obtained amount of carbon and the proportion of elemental carbon with respect to the total molecular weight of the organic acid compound (carbon content). In Examples and Comparative Examples, before the foregoing measurements, test pieces having yet to be applied with oil were each cut into the shape with a size of 2 cm×5 cm×0.8 mm (thickness). SPC materials of this size with clean surfaces were used as blanks. The amounts of carbon on surfaces of the blanks were measured in advance and confirmed to be zero.

(Analysis of Components in Lubricating Films: Inspection of Intensities of Organic Substances Present Between a Lubricating Film Surface and a Metal Material Surface)

The depth profiling analysis for components present between a surface of a lubricating film, as obtained in each of Examples and Comparative Examples to be described below, and a metal material was made in accordance with the following procedures to make evaluations.

The analysis method was employed in which elemental carbon distribution in a range from a surface of a lubricating film to a material (a wire rod or a cold rolled steel sheet) was analyzed by a Marcus-type glow discharge optical emission spectrometer (commonly called “GDS”; JY-5000RF, available from HORIBA).

A lubricating film obtained in each of Examples and Comparative Examples was sputtered with argon from the surface in the depth direction, and the intensity of each component was determined from the plasma emission specific to elemental carbon. In the measurement, the peak intensity derived from elemental carbon at the surface of a lubricating film (Is) and the peak intensity derived from elemental carbon at the middle level in the thickness direction of the lubricating film (Im) were first obtained, and then the ratio (Im/Is) was calculated.

Example 1

An aqueous solution of calcium complex was prepared using calcium nitrate, EDTA (disodium salt of ethylenediaminetetraacetic acid) and deionized water, and then isooctadecanoic acid was added thereto. The resultant solution was adjusted with ammonia and nitric acid to a pH of 5.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 1 with a calcium ion concentration of 2000 ppm by mass and an isooctadecanoic acid concentration of 2000 ppm by mass.

A 1 L graduated cylinder, serving as a treatment tank, was filled with the composition for direct-current cathodic electrolysis and heated to 25° C. A mesh member made of SUS, serving as the anode, was disposed in the treatment tank.

A wire rod having undergone surface cleaning treatment, serving as the cathode, was immersed in the center of the treatment tank, and the electrolysis operation was carried out at a current density of 10 A/dm² and an electric quantity of 20 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.). Since the current value was low, a zero resistance ammeter was disposed in the middle of the wiring to check that the current was flowing as specified during cathodic electrolysis.

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a lubricating film on the wire rod.

The lubricating film contained 0.3 g/m² of calcium (elemental calcium) and 0.2 g/m² of isooctadecanoic acid. The ratio (Im/Is) was 0.11.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied, as the weight thereof was being measured, to the wire rod of Example 1 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Example 2

An aqueous magnesium solution was prepared by adding magnesium nitrate to deionized water, and then nonanedioic acid was added thereto. The resultant solution was adjusted with ammonia and nitric acid to a pH of 9.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 2 with a magnesium ion concentration of 3000 ppm by mass and a nonanedioic acid concentration of 2000 ppm by mass.

A 1 L graduated cylinder, serving as a treatment tank, was filled with the composition for direct-current cathodic electrolysis and heated to 25° C. A mesh member made of SUS, serving as the anode, was disposed in the treatment tank.

A wire rod having undergone surface cleaning treatment, serving as the cathode, was immersed in the center of the treatment tank, and the electrolysis operation was carried out at a current density of 10 A/dm² and an electric quantity of 50 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.). Since the current value was low, a zero resistance ammeter was disposed in the middle of the wiring to check that the current was flowing as specified during cathodic electrolysis.

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a lubricating film on the wire rod.

The lubricating film contained 0.6 g/m² of magnesium (elemental magnesium) and 0.2 g/m² of nonanedioic acid. The ratio (Im/Is) was 0.11.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied, as the weight thereof was being measured, to the wire rod of Example 2 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Example 3

An aqueous solution of aluminum complex was prepared using aluminum nitrate, NTA (trisodium salt of nitrilotriacetic acid) and deionized water, and then nonanedioic acid was added thereto. The resultant solution was adjusted with ammonia and nitric acid to a pH of 6.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 3 with an aluminum ion concentration of 3000 ppm by mass and a nonanedioic acid concentration of 5000 ppm by mass.

A 1 L graduated cylinder, serving as a treatment tank, was filled with the composition for direct-current cathodic electrolysis and heated to 30° C. A mesh member made of SUS, serving as the anode, was disposed in the treatment tank.

A wire rod having undergone surface cleaning treatment, serving as the cathode, was immersed in the center of the treatment tank, and the electrolysis operation was carried out at a current density of 10 A/dm² and an electric quantity of 50 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.). Since the current value was low, a zero resistance ammeter was disposed in the middle of the wiring to check that the current was flowing as specified during cathodic electrolysis.

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a lubricating film on the wire rod.

The lubricating film contained 0.4 g/m² of aluminum (elemental aluminum) and 0.3 g/m² of nonanedioic acid. The ratio (Im/Is) was 0.13.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied, as the weight thereof was being measured, to the wire rod of Example 3 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Example 4

An aqueous yttrium solution was prepared using yttrium nitrate and deionized water, and then hexanedioic acid was added thereto. The resultant solution was adjusted with ammonia and nitric acid to a pH of 6.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 4 with an yttrium ion concentration of 3000 ppm by mass and a hexanedioic acid concentration of 5000 ppm by mass.

A 1 L graduated cylinder, serving as a treatment tank, was filled with the composition for direct-current cathodic electrolysis and heated to 30° C. A mesh member made of SUS, serving as the anode, was disposed in the treatment tank.

A wire rod having undergone surface cleaning treatment, serving as the cathode, was immersed in the center of the treatment tank, and the electrolysis operation was carried out at a current density of 20 A/dm² and an electric quantity of 50 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.). Since the current value was low, a zero resistance ammeter was disposed in the middle of the wiring to check that the current was flowing as specified during cathodic electrolysis.

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a lubricating film on the wire rod.

The lubricating film contained 0.7 g/m² of yttrium (elemental yttrium) and 0.3 g/m² of nonanedioic acid. The ratio (Im/Is) was 0.13.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied, as the weight thereof was being measured, to the wire rod of Example 4 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Example 5

An aqueous solution of calcium complex was prepared using calcium nitrate, EDTA (disodium salt of ethylenediaminetetraacetic acid) and deionized water, and then isooctadecanoic acid was added thereto. The resultant solution was adjusted with ammonia and nitric acid to a pH of 6.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 5 with a calcium ion concentration of 3000 ppm by mass and an isooctadecanoic acid concentration of 5000 ppm by mass.

A 1 L graduated cylinder, serving as a treatment tank, was filled with the composition for direct-current cathodic electrolysis and heated to 30° C. A mesh member made of SUS, serving as the anode, was disposed in the treatment tank.

A wire rod having undergone surface cleaning treatment, serving as the cathode, was immersed in the center of the treatment tank, and the electrolysis operation was carried out at a current density of 10 A/dm² and an electric quantity of 50 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.). Since the current value was low, a zero resistance ammeter was disposed in the middle of the wiring to check that the current was flowing as specified during cathodic electrolysis.

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a lubricating film on the wire rod.

The lubricating film contained 0.2 g/m² of calcium (elemental calcium) and 0.3 g/m² of isooctadecanoic acid. The ratio (Im/Is) was 0.13.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied, as the weight thereof was being measured, to the wire rod of Example 5 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Example 6

An aqueous magnesium solution was prepared using magnesium acetate and deionized water, and then nonanedioic acid was added thereto. The resultant solution was adjusted with ammonia and acetic acid to a pH of 9.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 6 with a magnesium ion concentration of 5000 ppm by mass and a nonanedioic acid concentration of 5000 ppm by mass.

A 5 L acrylic container (with inside dimensions of 31 cm long×12.6 cm wide×12.5 cm high) was filled with the composition for direct-current cathodic electrolysis of Example 6 and heated to 35° C. in a hot water bath. An insoluble anode (DSE for oxygen evolution, available from De Nora Permelec Ltd.) was disposed in the container in the longitudinal direction, while a cold rolled steel sheet having undergone surface cleaning treatment, serving as the cathode, was disposed in the center of the container. The anode and the cathode were positioned 15 cm away from each other, and the area ratio was adjusted by masking the anode so that the anode area was one third of the cathode area.

The electrolysis operation was carried out at a current density of 5 A/dm² and an electric quantity of 100 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.).

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a lubricating film on the cold rolled steel sheet.

The lubricating film contained 0.8 g/m² of magnesium (elemental magnesium) and 0.2 g/m² of nonanedioic acid. The ratio (Im/Is) was 0.11.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied by a roller to the cold rolled steel sheet of Example 6 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Example 7

An aqueous solution of aluminum complex was prepared using aluminum nitrate, NTA (trisodium salt of nitrilotriacetic acid) and deionized water, and then nonanedioic acid was added thereto. The resultant solution was adjusted with ammonia and nitric acid to a pH of 9.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 7 with an aluminum ion concentration of 2000 ppm by mass and a nonanedioic acid concentration of 7000 ppm by mass.

A 5 L acrylic container (with inside dimensions of 31 cm long×12.6 cm wide×12.5 cm high) was filled with the composition for direct-current cathodic electrolysis of Example 7 and heated to 35° C. in a hot water bath. An insoluble anode (DSE for oxygen evolution, available from De Nora Permelec Ltd.) was disposed in the container in the longitudinal direction, while a cold rolled steel sheet having undergone surface cleaning treatment, serving as the cathode, was disposed in the center of the container. The anode and the cathode were positioned 15 cm away from each other, and the area ratio was adjusted by masking the anode so that the anode area was one third of the cathode area.

The electrolysis operation was carried out at a current density of 5 A/dm² and an electric quantity of 100 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.).

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, applied with air by an air blower to remove water, thereby producing a lubricating film on the cold rolled steel sheet.

The lubricating film contained 0.2 g/m² of aluminum (elemental aluminum) and 0.3 g/m² of nonanedioic acid. The ratio (Im/Is) was 0.13.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied by a roller to the cold rolled steel sheet of Example 7 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Example 8

An aqueous yttrium solution was prepared using yttrium nitrate and deionized water, and then hexanedioic acid was added thereto. The resultant solution was adjusted with ammonia and nitric acid to a pH of 9.0, thereby obtaining a composition for direct-current cathodic electrolysis of Example 8 with an yttrium ion concentration of 3000 ppm by mass and a hexanedioic acid concentration of 7000 ppm by mass.

A 5 L acrylic container (with inside dimensions of 31 cm long×12.6 cm wide×12.5 cm high) was filled with the composition for direct-current cathodic electrolysis of Example 8 and heated to 35° C. in a hot water bath. An insoluble anode (DSE for oxygen evolution, available from De Nora Permelec Ltd.) was disposed in the container in the longitudinal direction, while a cold rolled steel sheet having undergone surface cleaning treatment, serving as the cathode, was disposed in the center of the container. The anode and the cathode were positioned 15 cm away from each other, and the area ratio was adjusted by masking the anode so that the anode area was one third of the cathode area.

The electrolysis operation was carried out at a current density of 5 A/dm² and an electric quantity of 20 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.).

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a lubricating film on the cold rolled steel sheet.

The lubricating film contained 0.2 g/m² of yttrium (elemental yttrium) and 0.5 g/m² of nonanedioic acid. The ratio (Im/Is) was 0.15.

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied by a roller to the cold rolled steel sheet of Example 8 on which the lubricating film has been formed, to a coating weight of 1.0 g/m².

Comparative Example 1

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied, as the weight thereof was being measured, to a wire rod to a coating weight of 1.0 g/m², thereby forming an oil layer on the wire rod.

Comparative Example 2

Anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was applied by a roll coater to a cold rolled steel sheet to a coating weight of 1.0 g/m², thereby forming an oil layer on the cold rolled steel sheet.

Comparative Example 3

A composition of Comparative Example 3 was prepared by adding magnesium azelate to deionized water. The composition was a white dispersion in which the sedimentation easily occurred.

A wire rod and a cold rolled steel sheet were immersed in this composition so that the composition was applied with a deposition amount of magnesium azelate of 2 g/m², and then carefully dried. After drying, the resultant films were white in color as a whole, while exhibiting unevenness in some places. In addition, whitish powder came off every time the wire rod and the cold rolled steel sheet were handled. On the grounds of this, it was easily foreseeable that the films should have poor adhesion to the wire rod and the cold rolled steel sheet. In this state, anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was carefully applied to a coating weight of 1.0 g/m².

This example is corresponding to an embodiment in which cathodic electrolysis is not performed.

Comparative Example 4

A composition of Comparative Example 4 was prepared by adding calcium stearate to deionized water. The composition was a white dispersion in which the sedimentation easily occurred.

A wire rod and a cold rolled steel sheet were immersed in this composition so that the composition was applied with a deposition amount of calcium stearate of 2 g/m², and then carefully dried. After drying, the resultant films were white in color as a whole, while exhibiting unevenness in some places. In addition, whitish powder came off every time the wire rod and the cold rolled steel sheet were handled. On the grounds of this, it was easily foreseeable that the films should have poor adhesion to the wire rod and the cold rolled steel sheet. In this state, anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was carefully applied to a coating weight of 1.0 g/m².

This example is corresponding to an embodiment in which cathodic electrolysis is not performed.

Comparative Example 5

A 1 L graduated cylinder, serving as a treatment tank, was filled with the composition of Example 1 of Patent Literature 1 (JP 2000-144494 A) and heated to 80° C. A mesh member made of SUS, serving as the anode, was disposed in the treatment tank.

An aqueous solution containing 3% by mass colloidal titanium-based surface conditioner (PREPALENE Z, available from Nihon Parkerizing Co., Ltd.) was prepared at normal temperature as described in Patent Literature 1, and a wire rod having undergone surface cleaning treatment was immersed in the solution for 1 minute. Thereafter, with the wire rod being disposed in the center of the treatment tank as the cathode, the electrolysis operation was carried out at a current density of 20 A/dm² and an electric quantity of 50 C/dm² with a rectifier (ZX-1600LA, available from Takasago, Ltd.). Since the current value was low, a zero resistance ammeter was disposed in the middle of the wiring to check that the current was flowing as specified during cathodic electrolysis.

Next, the test piece was taken out from the treatment tank, washed with clean water of Hiratsuka city, and applied with air by an air blower to remove water, thereby producing a zinc phosphate film on the wire rod.

To obtain the deposition amount of zinc phosphate film, the zinc phosphate film was dissolved and removed in a chromic acid solution heated to 75° C., and the difference in weight before and after the removal process was used to calculate the deposition amount. The deposition amount was 3.5 g/m² in terms of zinc phosphate.

Subsequently, anti-rust oil (NOX RUST 530F, available from Parker Industries, Inc.) was carefully applied to the wire rod to a coating weight of 1.0 g/m².

Comparative Example 6

The same operation as in Comparative Example 5 was carried out to obtain a wire rod having a zinc phosphate film with a deposition amount of zinc phosphate of 3.5 g/m².

Next, the wire rod was immersed in a reaction-type soap treatment solution (PALUBE 235, 70 g/L, available from Nihon Parkerizing Co., Ltd.) heated to 80° C., for 3 minutes. In this operation, due to the reaction caused by the reaction-type soap treatment, the deposited zinc phosphate was slightly dissolved to a deposition amount of 3.0 g/m². The total amount of metal soap and unreacted soap in a taken-out portion of the treatment solution was 3.0 g/m².

With the wire rods and the cold rolled steel sheets obtained in Examples and Comparative Examples as above, the following evaluation tests were carried out.

<Lubrication Evaluation>

When the test piece was a wire rod in Examples and Comparative Examples, the lubrication evaluation (No. 1) below was carried out, and when the test piece was a cold rolled steel sheet, the lubrication evaluation (No. 2) below was carried out, to evaluate the lubrication.

(Lubrication Evaluation (No. 1): Drawing Evaluation of Wire Rods)

Of each of the test pieces constituted of wire rods obtained in Examples and Comparative Examples, the end with a diameter of 3 mm was inserted into a cemented carbide die with a diameter of 3.05 mm (available from Fuji Die Co., Ltd.). Next, the wire rod was fixed to an upper grip of a precision universal tester (AG-X, available from Shimadzu Corporation), and the cemented carbide die was fixed to the tester. The upper grip was moved upward at a rate of 1 m/min to make the wire rod pass through the die. Drawing was thus carried out. The pulling load applied when the wire rod was passing through the die was monitored by a personal computer.

Based on the value of the pulling load for Comparative Example 1, the magnitudes of drawing loads for Examples and Comparative Examples were evaluated according to the following evaluation criteria. The evaluation for Comparative Example 1 was defined as “Poor.”

“Poor”: The pulling load was equal to or greater than that for Comparative Example 1. “Good”: The pulling load was less than that for Comparative Example 1 but not less than a half of that for Comparative Example 1. “Excellent”: The pulling load was less than a half of that for Comparative Example 1.

It is preferable that less scrap be generated at the entrance of the die in drawing. When scrap was not generated at the entrance of the die, the scrap generation suppressibility was determined to be “Good,” whereas when scrap was generated at the entrance of the die, the scrap generation suppressibility was determined to be “Poor.”

(Lubrication Evaluation (No. 2): Deep Drawing Evaluation of SPC Materials)

The test pieces constituted of cold rolled steel sheets obtained in Examples and Comparative Examples were blanked to a diameter of 110 mm to produce test pieces for deep drawing. Then, deep drawing was carried out using those test pieces with a high-speed deep drawing tester (DHV-20/650-8001, available from Tokyo Testing Machine Co., Ltd.). The high-speed deep drawing tester is roughly illustrated in FIG. 3. As shown in FIG. 3(A), a high-speed deep drawing tester 18 includes a punch 20 on which load is applied in a direction indicated by black arrow, and dies 22 to 28 supporting a test piece 30. The dies 24 and 28 are fixed. When load (blank holding load) is applied to the dies 22 and 26 in a direction indicated by white arrows, the both ends of the test piece 30 are fixed between the dies 22 and 24 and between the dies 26 and 28. After the test piece 30 is set in the tester 18, as shown in FIG. 3(B), load is applied to the punch 20 in the direction indicated by black arrow, blank holding load applied to keep the test piece 30 fixed is scanned, and the load when the test piece 30 is finally broken is checked.

Based on the value of the blank holding load for Comparative Example 2, the magnitudes of blank holding loads for Examples and Comparative Examples were evaluated according to the following evaluation criteria. The evaluation for Comparative Example 2 was defined as “Poor.”

“Poor”: The blank holding load was equal to or less than that for Comparative Example 2. “Good”: The blank holding load was greater than that for Comparative Example 2 but less than twice of that for Comparative Example 2. “Excellent”: The blank holding load was not less than twice of that for Comparative Example 2.

<Chemical Conversion Properties>

The chemical conversion property evaluations (No. 1) and (No. 2) below were conducted with the test pieces constituted of wire rods each having a lubricating film as produced in Examples 1 to 5 and Comparative Examples 5 and 6 and the test pieces constituted of cold rolled steel sheets each having a lubricating film as produced in Examples 6 to 8.

(Chemical Conversion Property Evaluation (No. 1): Examining Chemical Conversion Properties and Characteristics by Zinc Phosphate Treatment)

The test pieces were subjected to surface treatment often employed as surface preparation treatment for painting, in accordance with the following procedures.

(1) A degreasing agent (FINECLEANER E2001, available from Nihon Parkerizing Co., Ltd.) was heated to 43° C., and each test piece was immersed in the degreasing agent for 3 minutes to thereby remove a lubricating film and an oil layer on a surface of the test piece. (2) The degreasing agent was washed away from the test piece with clean water of Hiratsuka-city. (3) A surface conditioner (PREPALENE X, available from Nihon Parkerizing Co., Ltd.) was adjusted with clean water of Hiratsuka-city to 2 g/L, and the test piece was immersed in the thus-prepared surface conditioning solution for 30 seconds. (4) The test piece was taken out from the surface conditioning solution and then, with the surface conditioning solution remaining on the surface, immersed in a zinc phosphate treatment solution (PALBOND SX35, available from Nihon Parkerizing Co., Ltd.; free acidity: 0.7 pt; concentration of accelerator (accelerator 131, available from Nihon Parkerizing Co., Ltd.): 3.5 pt) with shaking for 2 minutes. (5) After the zinc phosphate treatment, the test piece was washed with clean water of Hiratsuka city and further washed with deionized water. Thereafter, air was applied by an air blower to remove water.

The evenness of a zinc phosphate film was visually evaluated. The evenness was determined to be “Excellent” when the color was uniform and no unevenness was found, i.e., the evenness was satisfactory, “Good” when no unevenness was visually found, and “Poor” when the unevenness was found because this may lead to uneven paint.

(Chemical Conversion Property Evaluation (No. 2): Examining Chemical Conversion Properties and Characteristics by Metal Oxide Treatment)

The test pieces were subjected to surface treatment widely employed as surface preparation treatment for painting, in accordance with the following procedures.

(1) A degreasing agent (FINECLEANER E2001, available from Nihon Parkerizing Co., Ltd.) was heated to 43° C., and each test piece was immersed in the degreasing agent for 3 minutes to thereby remove a lubricating film and an oil layer on a surface of the test piece. (2) The degreasing agent was washed away from the test piece with clean water of Hiratsuka-city. (3) The test piece was immersed in a treatment solution for metal oxide (PALLUCID 1500, available from Nihon Parkerizing Co., Ltd.; pH 4.0) adjusted to 45° C. with shaking for 2 minutes. (4) After the treatment, the test piece was washed with clean water of Hiratsuka city and further washed with deionized water. Thereafter, air was applied by an air blower to remove water.

The evenness of a metal oxide film was visually evaluated. The evenness was determined to be “Excellent” when the color was uniform and no unevenness was found, i.e., the evenness was satisfactory, “Good” when no unevenness was visually found, and “Poor” when the unevenness was found because this may lead to uneven paint.

The evaluation results are all shown in Table 1.

In Table 1, “Ratio (Is/Im)” refers to the ratio (Im/Is) between the peak intensity derived from elemental carbon at the surface of the lubricating film opposite from the metal material side (Is) and the peak intensity derived from elemental carbon at the middle level in the lubricating film corresponding to a half of the whole thickness of the lubricating film from the surface opposite from the metal material side (Im).

The value of “Ratio (Is/Im)” of “Lubricating film” for Comparative Example 6 in Table 1 represents the ratio (Is/Im) obtained with a film formed by reaction-type metal soap treatment, and a zinc phosphate film is not considered.

For Comparative Examples 5 and 6, values in “Metal element” fields in Table 1 represent the amounts of zinc phosphate, and values in “Organic acid compound” fields represent the amounts of films formed by reaction-type metal soap treatment.

In “Lubrication evaluation” fields in Table 1, “−” means that no evaluation was conducted.

TABLE 1 Composition Concentration Concentration of of metal ion organic acid Type of (ppm by IUPAC name of organic compound Chelating Temp. Standard metal ion mass) acid compound (ppm by mass) agent (° C.) pH Example 1 Ca 2000 Isooctadecanoic acid 2000 EDTA 25.0 5.0 2 Mg 3000 Nonanedioic acid 2000 — 25.0 9.0 3 Al 3000 Nonanedioic acid 5000 NTA 30.0 6.0 4 Y 3000 Hexanedioic acid 5000 — 30.0 6.0 5 Ca 3000 Isooctadecanoic acid 5000 EDTA 30.0 6.0 6 Mg 5000 Nonanedioic acid 5000 — 35.0 9.0 7 Al 2000 Nonanedioic acid 7000 NTA 35.0 9.0 8 Y 3000 Hexanedioic acid 7000 — 35.0 8.0 Comparative 1 Wire rod, untreated, oil applied example 2 Sheet type, SPC, oil applied 3 Immersed in a magnesium azelate dispersion to 25.0 6.0 apply magnesium azelate in an amount of 2 g/m², and then dried 4 Immersed in a calcium stearate dispersion to 25.0 6.0 apply calcium stearate in an amount of 2 g/m², and then dried 5 Deposition by cathodic electrolysis, 80.0 1.0 zinc phosphate (embodiment of Patent Literature 1) 6 Deposition by cathodic electrolysis, 80.0 1.0 zinc phosphate + reaction-type metal soap treatment (second step, 80° C.) Lubricating film Chemical conversion Organic Lubrication evaluation property evaluation Metal acid Lubrication Scrap Lubrication Zinc Metal element compound Ratio evaluation generation evaluation phosphate oxide Standard g/m² g/m² (Im/Is) (No. 1) suppressibility (No. 2) treatment treatment Example 1 0.3 0.2 0.11 Good Good — Excellent Excellent 2 0.6 0.2 0.11 Good Good — Excellent Excellent 3 0.4 0.3 0.13 Good Good — Good Excellent 4 0.7 0.3 0.13 Good Good — Good Good 5 0.2 0.3 0.13 Good Good — Excellent Excellent 6 0.8 0.2 0.11 — Excellent Excellent Excellent 7 0.2 0.3 0.13 — Excellent Good Excellent 8 0.2 0.5 0.15 — Excellent Good Good Comparative 1 Wire rod, untreated, Poor Good — Good Good example oil applied 2 Sheet type, SPC, — — Poor Good Good oil applied 3 0.2 1.8 1 Poor Poor Poor Good Good 4 0.4 1.6 1 Poor Poor Poor Good Good 5 3.5 0.0 — Good Good — Poor Poor 6 3.0 3.0 1 Excellent x — Poor Poor

As can be seen in Table 1, the lubricating films obtained by cathodic electrolysis using the composition of the invention exhibited excellent lubrication as well as allowing excellent chemical conversion properties to be achieved after degreasing.

In contrast, in Comparative Examples 1 and 2 in each of which only an oil layer was provided, Comparative Examples 3 and 4 in each of which cathodic electrolysis was not performed, and Comparative Examples 5 and 6 corresponding to embodiments of Patent Literature 1, desired effects were not achieved.

REFERENCE SIGNS LIST

-   -   10, 100 metal material having lubricating film     -   12 metal material     -   14 lubricating film     -   16 oil layer     -   18 high-speed deep drawing tester     -   20 punch     -   22, 24, 26, 28 die     -   30 test piece 

1-8. (canceled)
 9. A composition for direct-current cathodic electrolysis, comprising: (A) at least one type of metal ion, or its complex, selected from the group consisting of divalent or higher valent main group metal ions (excluding zinc ion) and rare earth element ions; (B) an organic acid compound having a carboxyl group and a linear alkylene group with 4 or more carbon atoms per molecule; and (C) water.
 10. The composition for direct-current cathodic electrolysis according to claim 9, wherein the metal ion or its complex (A) includes at least one type of metal ion, or its complex, selected from the group consisting of magnesium ion, calcium ion, aluminum ion, yttrium ion and lanthanoid metal ions.
 11. The composition for direct-current cathodic electrolysis according to claim 9, wherein the organic acid compound (B) includes an aliphatic monocarboxylic acid having a linear alkylene group with 4 or more carbon atoms or an aliphatic dicarboxylic acid having a linear alkylene group with 4 or more carbon atoms.
 12. The composition for direct-current cathodic electrolysis according to claim 10, wherein the organic acid compound (B) includes an aliphatic monocarboxylic acid having a linear alkylene group with 4 or more carbon atoms or an aliphatic dicarboxylic acid having a linear alkylene group with 4 or more carbon atoms.
 13. The composition for direct-current cathodic electrolysis according to claim 9, having a pH of 3.5 to 12.5.
 14. The composition for direct-current cathodic electrolysis according to claim 10, having a pH of 3.5 to 12.5.
 15. The composition for direct-current cathodic electrolysis according to claim 11, having a pH of 3.5 to 12.5.
 16. The composition for direct-current cathodic electrolysis according to claim 12, having a pH of 3.5 to 12.5.
 17. A method of producing a metal material having a lubricating film, comprising a step of forming a lubricating film on a surface of a metal material by immersing the metal material in a composition for direct-current cathodic electrolysis and performing cathodic electrolysis using direct current with the metal material serving as a cathode, wherein the composition for direct-current cathodic electrolysis includes: (A) at least one type of metal ion, or its complex, selected from the group consisting of divalent or higher valent main group metal ions (excluding zinc ion) and rare earth element ions; (B) an organic acid compound having a carboxyl group and a linear alkylene group with 4 or more carbon atoms per molecule; and (C) water.
 18. The method of producing a metal material having a lubricating film according to claim 17, wherein the metal ion or its complex (A) includes at least one type of metal ion, or its complex, selected from the group consisting of magnesium ion, calcium ion, aluminum ion, yttrium ion and lanthanoid metal ions.
 19. The method of producing a metal material having a lubricating film according to claim 17, wherein the organic acid compound (B) includes an aliphatic monocarboxylic acid having a linear alkylene group with 4 or more carbon atoms or an aliphatic dicarboxylic acid having a linear alkylene group with 4 or more carbon atoms.
 20. The method of producing a metal material having a lubricating film according to claim 18, wherein the organic acid compound (B) includes an aliphatic monocarboxylic acid having a linear alkylene group with 4 or more carbon atoms or an aliphatic dicarboxylic acid having a linear alkylene group with 4 or more carbon atoms.
 21. The method of producing a metal material having a lubricating film according to claim 17, wherein the composition for direct-current cathodic electrolysis has a pH of 3.5 to 12.5.
 22. The method of producing a metal material having a lubricating film according to claim 18, wherein the composition for direct-current cathodic electrolysis has a pH of 3.5 to 12.5.
 23. The method of producing a metal material having a lubricating film according to claim 19, wherein the composition for direct-current cathodic electrolysis has a pH of 3.5 to 12.5.
 24. The method of producing a metal material having a lubricating film according to claim 20, wherein the composition for direct-current cathodic electrolysis has a pH of 3.5 to 12.5.
 25. A metal material having a lubricating film comprising a metal material and a lubricating film disposed on a surface of the metal material, wherein the lubricating film includes: at least one type of metal element selected from the group consisting of divalent or higher valent main group metal elements (excluding elemental zinc) and rare earth elements; and an organic acid compound having a carboxyl group and a linear alkylene group with 4 or more carbon atoms per molecule, and/or its salt, and wherein in a depth profiling analysis of the lubricating film by glow discharge optical emission spectrometry as conducted on the lubricating film from its surface opposite from a side facing the metal material in a direction toward the metal material, a ratio (Im/Is) between a peak intensity derived from elemental carbon at the surface of the lubricating film opposite from the side facing the metal material (Is) and a peak intensity derived from elemental carbon at a middle level in the lubricating film corresponding to a half of a whole thickness of the lubricating film from the surface opposite from the side facing the metal material (Im) is less than 1.0.
 26. The metal material having a lubricating film according to claim 25, further comprising, on the lubricating film, an oil layer containing an oil component. 